Method of making resistance elements



Oct. 13, 1936. R H. HOBROCK 2,057,431 7 METHOD OF MAKING RESISTANCE ELEMENTS Filed March 29, 1933 FIG.

Patented a. 1a, 1936' UNITED STATES METHOD OF MAKING RESISTANCE ELEMENTS Raymond E. Hobrock, Akron, Ohio Application March 29, 1933, Serial No. 683,38!

Claims.

My invention relates to resistance elements and a method of making resistance elements.

Many attempts have been made heretofore to produce resistance elements by mechanically 5 mixing finely divided carbon particles with ceramic materials and forming the mixture into rods or blocks which are then fused into ceramic resistance elements. This procedure requires prolonged mixing of the materials and the resulting resistance elements have many undesirable electrical characteristics.

An object of the present invention is to provide an effective and efficient resistance element and a simple and economical method of making such an element.

A further object is to provide a resistance element which has a substantially straight line voltage current characteristic.

A further object is to provide a thermo-chemical method of incorporating carbon particles in a. ceramic base.

Other objects and advantages will appear as the description proceeds.

In accordance with one embodiment of the invention, a ceramic article or rod is placed in an atmosphere of a hydrocarbon gas and heated to the disassociation temperature of the gas whereupon the precipitated carbon permeates the ceramic article to form a resistance element thereof.

A complete understanding of the invention may be had by reference to the following description taken in conjunction with the accompanying drawing, in which Fig. 1 is a sectional view, partly diagrammatic, of an apparatus for practicing the method and making articles of this invention;

Fig. 2 is a sectional view, partly diagrammatic,

- of an apparatus for applying terminals to resistance elements; and

Fig. 3 is a perspective view of a resistance element embodying the invention.

The base of the resistance element of this invention consists of a porous insulating body 5 preferably of a ceramic material. In'order to impregnate or saturate such bodies with carbon, a number of such bodies are fed into a tube 6 of a furnace I. This tube is preferably made of resistance material, such as a nickel chromium alloy known as nichrome and is heated by passing an electric current therethrough from a source not shown. The amount of current passing therethrough may be regulated by means of a. variable resistance 8. Surrounding the tube 6 is an enclosed air space formed by a second tube 9 of a refractory insulating material, such as Silmanite. A winding II of resistance material is wound about the tube 9 and is connected to the secondary of a transformer 12 for passing a current through the winding to supplement the heating of the tube 6. The secondary of the transformer has a variable resistance 13 therein to control the current in the winding I I.

It has been found that when a number of bodies to be impregnated with carbon are fed into the tube 6 and are heated to the desired temperature at the entrance end of the tube, they will attain too high a. temperature before reaching the exit end unless some means is provided to reduce the amount of heat supplied to the bodies after they reach the desired temperature. This difficulty is overcome by spacing the convolutions of the winding ll closely together at the entrance end of the tube to quickly bring the bodies to the desired temperature and spacing the convolutions farther apart in that portion of the tube where the bodies have reached the desired temperature.

Surrounding the tube 9 and spaced therefrom is a casing H which is filled with heat insulating material l5, such as asbestos wool or the like.

The tube 6 projects from both ends of the easing and is preferably tilted to aid in feeding the elements to be treated therethrough. At the lower end of tube 6 a. supply tube I6 is connected thereto for supplying a carbon compound, such as a hydrocarbon gas, to the tube 6. Any suitable gas, may be used, such as ordinary illuminating gas, methane, propane, water gas, and the like.

In order to prevent too large a portion of the gas from escaping from the lower end of the tube,

a baflle I1 is placed in this end of the tube so that substantially an equal amount of gas escapes from each end. The escaping gas is ignited at each end of the tube and forms a flame seal to prevent air from entering the ends of the tube.

The elements to be impregnated may be placed in a chute i8 and are fed successively into the furnace by a reciprocating plunger l9 which may be actuated by an eccentric 2| driven by a source of power not shown. As the elements enter the furnace, they are raised to a high temperature and the gas in the furnace is heated to its disassociation temperature to precipitate nascent carbon which permeates the elements. The resistance of the elements may be controlled by the amount of carbon absorbed thereby depending upon the time the elements are in the furnace.

In order to use the resistance elements in a circult, caps of conducting material may be pressed over the ends thereof or soldered thereto. A conducting surface or terminal may also be formed on each end of an element by cathode sputtering. For this purpose a number of elements are placed in a receptacle 22 with the upper ends of the elements exposed. The receptacle is then placed in a bell II resting on a base '24. The upper end of the bell is provided with a silver, copper, or

I gold electrode II and the bell is evacuated through a tube 2!. This tube has an oiiset portion 21 which has a second electrode 2| therein. After the bell is evacuated. a high potential is applied to the electrodes through a transformer 20, causing metal from electrode 2| to be deposed on the upper ends of the resistance elements in a thin layer. The lower ends or the elements are then provided with metal layers in the same manner. Terminal members may then be soldered, clamped or otherwise secured to the metal layers on the ends of the resistance elements. Another method of securing terminals to the resistance elements is to metal spray the ends by a process well known in the art and then soldering terminal members thereto.

It will be understood that the nature and embodiments oi' the invention herein described and illustrated are merely illustrative of the invention and that many changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

. hydrocarbon atmosphere of the methane series containing molecular carbon to impregnate the article throughout.

4. A method of making a resistance element, which comprises generating nascent carbon from a hydrocarbon gas of the methane series and impregnating a porous insulating body therewith to a substantial depth.

5. A method of making a resistance element which comprises heating a ceramic body in an atmosphere of a hydrocarbon oi the methane series capable of precipitating carbon in a iorm to impregnate said body throughout.

RAYMOND H. HOBROC K. 

